This invention relates to an apparatus for sensing the distance between an object of electrically conductive material and a reference point, said apparatus comprising an electrode with a tip forming the reference point.
Distance and position sensors of various types are well known. Some of these apparatus are utilized especially in so-called seam followers for mechanized or automated welding where they sense the distance to or the position of a seam and transmit signals responsive thereto to a signal transducer converting said signals into signals for controlling servo units. These servo units are connected to a holder, such as crossing slides carrying a welding gun, and control the adjustment of said holder and thus the position of the welding gun relative to the seam.
Seam followers of this type may be characterized according to the sensing principle which is utilized, i.e. according to the type of sensor or transducer, and in this respect one distinguishes between contact transducers and contactless transducers. Contactless transducers are transducers establishing an electric or mechanical contact with the object and thus are no distance sensors. Distance sensors are contactless. Examples of contactless transducers are inductive and capacitive transducers.
The main object of this invention is to provide a relatively simple and inexpensive, but nevertheless reliable apparatus for sensing the distance between an object of electrically conductive material and a reference point.
A further object of this invention is to provide a distance sensor which is well suited for use in a contactless seam follower for mechanized or automated welding. A further object of this invention is to provide a distance sensor which, in contrast to, for example, certain types of capacitive and inductive transducers, requires a very small measuring surface on the object and which, when used in connection with a seam follower of the above-mentioned type, can be disposed close to the welding gun.
According to the invention, these objects are realized by means of an apparatus which is of the abovementioned type and is characterized by a high voltage source to which the electrode is connected via a supply line and which is adapted to generate high voltage pulses for generating an arc between the electrode tip and the object, and a measuring means which is adapted to sense the electric field around the supply line and to transmit a measuring signal proportional to said field and is connected to a measuring signal sensing circuit.
In a preferred embodiment of the invention, the measuring means is an air-cored measuring coil, one end of which is free, while the other end is connected to the measuring signal sensing circuit. In the preferred embodiment, the measuring coil furthermore is disposed around the supply line, and the measuring signal sensing circuit comprises a comparator unit adapted to compare the measuring signal to a signal corresponding to a predetermined distance between the object and the electrode point.